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Ernest Rutherford and the Atom article

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Introduction

Imagining Science

Ernest Rutherford – The nuclear atom

Today we’re going to be looking at Rutherford’s alpha-particle scattering experiment and how, through this, he found ground-breaking new evidence on the structure of a nuclear atom.

Ernest Rutherford, a notable English physicist, in the 20th century understood that all matter is made up of atoms. However, he wanted to delve deeper in this understanding about atoms. As a result in 1909, along with his assistants, Hans Geiger and Ernest Marsden, carried out an experiment  to investigate a detailed model for the atom (the ‘inner-workings’).

Diagram of Rutherford’s Alpha-Particle Scattering Experiment

image00.jpg

What Rutherford did was quite unique. He used and a He used a source which emitted alpha particles (charged helium ions), and directed the beam of alpha particles towards a thin gold foil (he wanted a thin layer as thin a layer as possible) to observe any effects between the two.

Rutherford’s Observations

  • Roughly 99% of the alpha particles passed straight through the foil.
  • Some of the alpha particles were deflected by the foil at small angles - 1 in 8000 alpha particles were deflected at around 90° and over.
  • Around one out of every 12000 particles to rebounded off the gold foil – some directly in the opposite direction!
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Middle

Rutherford stated that:

“It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”

Rutherford’s Explanation about the Observations

Rutherford inferred from the observations that there must be a positive charge in the atom due to the fact that the alpha particles, which were repelled, were positively-charged (as similar charges repel each other and cause them to scatter in the opposite/a different direction. Also, the observations implied that the ‘positively-charged something’ in the atom must also have a high mass. The high mass, within the atom, enabled the ‘something’ to withstand the charged alpha particles that were fired onto the foil at such energy – if it did not have a high mass then no alpha particles would have been deflected.

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Conclusion

His explanations could be tested in different ways. What can be done is by testing the explanation with different foils. In today’s day-and-age, science has advanced much more than in Rutherford’s time. Through this, different (positively-charged) particles can be used to fire at different types of foils to see if the explanation is true for all. As all matter is made of atoms, then the observations in the different explanations must be similar to that of Rutherford’s observations. Predictions can be made through this – i.e. by stating that particles should deflect or rebound or pass through when fired. Also, predictions can be made by seeing what to expect when using an electron microscope to outline some-type of structure within the atom. At a specialist-research facility in Switzerland (CERN), they use particle-accelerators in order to make atoms collide. This enables scientists to see the structure within. All of this can be done by making predictions about the structure of atoms using Rutherford’s explanation about the nuclear model of an atom.

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